Who knew fans would pay $250 for copies of the colorful shirts worn by former sports stars?

Just four months earlier, he had been hustling from one Philadelphia hair salon to the next, selling pound cake to women while they were being coiffed. Now Reuben Harley was reclining on a black leather couch in the midtown Manhattan recording studio of hip-hop mogul Sean (P. Diddy) Combs. The unlikely pair chatted about business, music and, most importantly, jerseys--the classic models that sports legends like Julius Erving, Nolan Ryan and Jackie Robinson used to wear.

Harley, then 27, was the new marketing director for Mitchell & Ness Nostalgia Co., which lovingly sewed and sold authentic replicas of old sports...